With winter firmly entrenched and some residents seeking alternative means to heat their homes, garages and other work spaces, they must be wary of the silent killer.

Carbon monoxide is an odorless, colorless and tasteless gas produced by some heating devices. In small concentrations, it presents no health hazard. However, in greater concentrations, it can lead to death.

According to Capt. Joe Fowler of the Cambridge Fire Department, firefighters have responded to numerous calls for CO checks since the heating season began. No fatalities have been reported, but residents must still take care to prevent sickness or death due to poisoning from the gas.

The gas is produced through the incomplete burning of solid, liquid and gaseous fuels, including natural gas, charcoal, wood, kerosene and coal. All well, automobile engines produce CO while running.

Making the gas so dangerous is its tendency to be absorbed into the bloodstream more readily than oxygen.

Fowler said most of their CO checks are performed on hot water tanks, furnaces and portable sources of heat.

Symptoms of exposure to CO concentrations are generally flu-like, without the fever. They include headache, fatigue, shortness of breath, nausea and dizziness.

In some cases, a misdiagnosis of CO poisoning as the flu has lead to death.

Concentrations of CO are measured in parts per million. According to the Occupational Safety Health Administration, 35 ppm is the maximum allowable exposure during an eight hour period. Other concentrations and their effects include:

100 ppm Maximum concentration in which a person of normal health will not experience symptoms

200 ppm Slight headache, tiredness, dizziness after 2 or 3 hours

300 ppm Maximum exposure allowed by OSHA for any person at a given time

400 ppm Life threatening after 3 hours exposure

800 ppm Dizziness, nausea, convulsions within 45 minutes; death within three hours

6,400 ppm Dizziness, nausea, convulsions within 1 to 2 minutes; death within 10 to 15 minutes.

Fowler said residents using alternate heating devices should ensure proper ventilation in any space in which they are used.

Other tips to avoid CO poisoning include not leaving automobiles to idle in a garage, even with the garage door open, avoiding the use of gasoline-powered tools in an enclosed space and the installation of a CO detector.

For more information, contact Cambridge firefighters at 432-3232, or any area volunteer fire department.